Tiltrotor aircraft typically include multiple propulsion assemblies that are positioned near the outboard ends of a wing. Each propulsion assembly may include an engine and transmission that provide torque and rotational energy to a drive shaft that rotates a proprotor assembly including a hub assembly and a plurality of proprotor blades. Typically, a pylon assembly, which includes the proprotor assembly, is rotatable relative to the wing such that the proprotor blades have a generally horizontal plane of rotation providing vertical lift for takeoff, hovering and landing, much like a conventional helicopter, and a generally vertical plane of rotation providing forward thrust for cruising in forward flight with the wing providing lift, much like a conventional propeller driven airplane. In addition, tiltrotor aircraft can be operated in configurations between the helicopter flight mode and the airplane flight mode, which may be referred to as conversion flight mode.
In conventional tiltrotor aircraft, each nacelle that houses an engine and a transmission is also rotatable relative to the wing. Such nacelles rotate about a spindle that is inserted or stabbed into an outboard end of the wing. It has been found, however, that certain structural and aerodynamic advantages may be obtained by fixedly (i.e., non-rotatably) coupling the nacelles to the wing. To optimize the manufacture of such fixed nacelle tiltrotor aircraft, it may be useful to assemble the fixed nacelles in parallel with the wing to decrease the overall assembly time and cost of the tiltrotor aircraft. After separate assembly, the joint between the fixed nacelles and wing must withstand the high forces experienced during flight. Accordingly, a need has arisen for a stable and reliable interface between the wing and fixed nacelles of a tiltrotor aircraft.